How do I get strong extra curriculars while doing the things I love?

First of all, you're a freshman, so you have 2-3 years to get everything figured out. It's a good thing that you know what you like doing. I think it's a misconception that you have to do science clubs, science competitions, shadowing, and research in order to get into medical school, but you do want to find some more professional/competitive interests in order to stand out. If I were you, since you like volunteering, I would consider shadowing/interning/volunteering at a hospital once COVID lockdowns are over. Not only is it something you're interested in, but it can help you decide whether you actually want to be a doctor.

Since you're relatively new to your school, try going to writing clubs, book clubs, or writing competitions at or near your school. I understand wanting to keep your private interests private, but if you do want to share your writing, entering statewide/nationwide competitions is a great way to show your passions to college admissions. It doesn't matter if ALL your ECs are directly related to medicine, colleges just want to see passionate people with unique interests.

Hope this helps! Let me know if you have any questions.

Since your going to be a STEM major, focus your effort there. Quality matters more than quantity and as such, getting a leadership or big role in a STEM area will look great. I'd recommend trying to get into the Regeneron Talent Search Program. It's previous winners involve future Noble prize winners and is seen as a great predictor of someone's future. You only have one chance at winning it (since it takes place during your senior year), so start on research as early as possible. The Telluride Summer Association Program is known as "The Key to the Ivies" and is a free program that is known to recruit students with "The Ivy Mindset" already. I wouldn't recommend shoving aside other programs like the VFW Voice of Democracy which offers scholarships. For your Sophmore, join a program you'd like to stay in for the rest of high school (such as Science Olympiad) so you can show colleges you can put effort and time into an area but staying with it gives you more chances to get a leadership role. When you hit Junior year, drop that unnecessary extra-circulars and focus on STEM only.